1. Field of the Invention
This invention relates to a method for preparing a cellulose acetate filter rod useful as a cigarette filter. More particularly, this invention relates to a method for preparing a cellulose acetate filter rod which comprises adding a plasticizer containing 1,4-butanediol diacetate to cellulose acetate fibers.
2. Description of the Prior Art
Plasticizers for cellulose acetate rods, which are useful as tobacco smoke filters, are essential because such plasticizers dissolve or partially dissolve the cellulose acetate fibers at the places where they contact each other and, as a result of curing, the fibers mutually unite at their random points of contact, whereby the united fibers maintain the shape of the resulting rod, give the rod a suitable hardness and impart to the rod itself the hardness required so that the rod can be cut into tobacco smoke filters, such as cigarette filters.
In general, triacetin, the diacetate, dipropionate, and dibutyrate esters of triethyleneglycol, dimethoxyethyl phthalate, and triethyl citrate are used as plasticizers for cellulose acetate fibers constituting cigarette filters. However, when triethyl citrate and dimethoxyethyl phthalate are used, it is necessary to heat the fiber rods at a high temperature above room temperature for 2 to 4 hours in the step of curing the rods.
The diacetate, dipropionate and dibutyrate esters of triethyleneglycol can confer sufficient hardness on the rods, when cured at room temperature for a relatively short time, but the resulting filters are not satisfactory with respect to the cigarette flavor and smoking taste.
We have previously discovered that 1,3-butanediol diacetate is a plasticizer which is excellent in plasticizing effect on cellulose acetate fibers and which does not harm the cigarette flavor and smoking taste, as described in our Japanese Patent application No. 1974-36,899 (unexamined). However, that compound is defective because it has a low boiling point and a peculiar odor and, therefore, it is difficult to employ in practice.
Also, the plugmaking machine itself has been greatly improved so that its tape speed has become remarkably high. Thus, the tape speed of a Hauni KDF-2 plugmaker is 400 m/min., and this is approximately twice as high as that in conventional machines and it is likely that this speed will further increase.
In view of these circumstances, the long curing time required with conventional plasticizers to achieve the necessary rod hardness causes serious problems in practical use.